1. Field of the Invention
The present invention relates to a recording head used as a recording head for conducting printing onto a recording medium, the recording head having an energy converting element for converting electric energy into printing energy, and a manufacturing method thereof. More particularly, the invention relates to a substrate for a recording head, which is a semiconductor substrate having a printing energy generating element for generating printing energy and a manufacturing method thereof.
In this specification, printing onto a recording medium shall include not only operations of printing of characters, but also printing operations of images other than characters such as symbols and graphics.
2. Description of the Related Art
There is conventionally known an ink-jet recording method called the bubble-jet recording method comprising the steps of causing a change in state in ink leading to a steep change in volume (occurrence of bubbles) by imparting energy such as heat to a liquid such as ink, discharging the ink from a discharge port under the effect of a working force resulting from the change in state, and forming an image by depositing the discharged ink onto a recording medium. A recording apparatus based on this bubble-jet recording method usually comprises, as disclosed in U.S. Pat. No. 4,723,129, a discharge port for discharging ink, an ink channel communicating with the discharge port, and a heating resistor serving as an energy converting element for discharging the ink, arranged in the ink channel.
According to such a recording method, it is possible to record a high-quality image at a high speed with low noise, and in a head carrying out this recording method, it is possible to arrange discharge ports for discharging ink at a high density. This recording method therefore provides many advantages including a recorded image of a high resolution available with a compact apparatus, and the possibility to easily obtain a color image. The bubble-jet recording method has therefore been popularly used in recent years in many office machines such as a printer, a copying machine and a facsimile machine, and the uses thereof now cover industrial systems including a textile printing apparatus.
A heating resistor for producing energy for discharging ink is manufacturable by means of a semiconductor manufacturing process. A conventional head based on the bubble-jet technology therefore has a configuration in which a covering plate made of a resin such as polysulfone or glass having a groove for forming an ink channel formed thereon is bonded onto an element substrate (a substrate for a recording head) comprising a silicon substrate having a heating resistor formed thereon.
In some such conventional heads, by use of the fact that the element substrate comprises a silicon substrate, in addition to the heating resistor formed on the element substrate, a driver for driving the heating resistor, a temperature sensor used when controlling the heating resistor in response to the head temperature, or a driving controller is arranged on the element substrate (Japanese Patent. Application Laid-Open No. 7-52387, etc.). A bead thus having a driver, a temperature sensor and a drive controller thereof has already been industrialized, contributing to improvement of reliability of recording heads and downsizing of apparatuses.
A configuration in which an element substrate 101 serving as a substrate for a recording head is arranged on a supporting plate 102 of the recording head is illustrated in FIG. 10. The element substrate 101 and a wiring substrate 105 are arranged on the recording head supporting plate 102, and the element substrate 101 and the wiring substrate 105 are bonded by wire bonding. A contact pad 106 for connecting to a printer main body is provided on the wiring substrate 105.
A configuration of the circuit element formed on the element substrate 101 is illustrated in a block diagram of FIG. 11. As shown in FIG. 11, a beater section 201, a driving circuit section 202, a retaining circuit section 203, a transfer circuit section 204, a voltage drop circuit section 905, a rank resistance measuring circuit section 906, and a temperature measuring circuit section 907 are formed on the element substrate 101.
The heater section 201 is composed of a plurality of heating resistors. The transfer circuit section 204 is composed of a shift register and the like, and converts serial data for printing into parallel data by sequentially transferring the same. The retaining circuit section 203 is a circuit for latching and retaining the parallel data converted by the transfer circuit section 204. The driving circuit section 202 individually drives the heating resistors of the heater section 201 on the basis of the data latched by the retaining circuit section 204. A reset signal 210 for achieving a standby state of a printing operation is entered in the retaining circuit section 203, and the retaining circuit section 203 outputs a data for prohibiting the driving circuit section 202 from operating when the reset signal 210 is active on a high level (hereinafter denoted as xe2x80x9cHxe2x80x9d).
The voltage drop circuit section 905 is a circuit that outputs a voltage value of a beater driving power source VH by reducing the same by a certain value. The rank resistance measuring circuit section 906 is a circuit for measuring a resistance value of the rank resistance formed on the element substrate 101. The rank resistance as herein used is a resistance provided for measuring dispersion in manufacturing of the resistance values of the heating resistors formed in the heater section 201, provided separately from the other circuits, only for measuring resistance values. The temperature measuring circuit section 907 is for measuring temperature of an ink-jet head, being a sensor for measuring the ink temperature. Measurement of the ink temperature is based on the fact that the positive-direction voltage of a diode varies with temperature.
Typical circuit configurations of the voltage drop circuit section 905, the driving circuit section 202, and the heater section 201 are illustrated in FIG. 12.
The voltage drop circuit section 905 comprises resistances 21, 22 and 24, and an N-channel MOS transistor 23. The heater section 201 is composed of a plurality of heating resistors 50. In the driving circuit section 202, a resistance 25, N-channel MOS transistors 26 to 28 and a P-channel MOS transistor 29 are provided for one heating resistor 50 of the heater section 201.
The voltage drop circuit section 905 divides the entered heater power source VH by the resistances 21 and 22 into a certain voltage, and outputs a voltage lower than the thus divided voltage by a threshold value voltage of the N-channel MOS transistor 23. Because the heater power source VH has been divided by the resistances 21 and 22, a constant current to flows in the voltage drop circuit section 905, irrespective of the operating state of the recording head, i.e., the operating state of the heater serving as an energy converting element for converting electric energy into printing energy.
The driving circuit section 202 on/off-controls the N-channel MOS transistor 28 on the basis of data held in the retaining circuit section 203 and drives the heating resistors 50. The term xe2x80x9cconstant currentxe2x80x9d as herein used means a constant current flowing into circuits without being affected by the output state or the like, upon impression of the source voltage in a normal operating state. The constant current is used as a reference current in the above-mentioned circuits.
The voltage drop circuit section 905 for outputting the heater power source VH after reducing it by a prescribed value is provided for the following reasons.
Since the heater power source VH impressed onto the heating resistors 50 has a higher voltage than a logic power source VDD, the N-channel MOS transistor 28 is required to have a high driving capability for driving the heating resistors 50. It is, however, difficult to achieve a sufficient driving capability by directly impressing a logic signal of only the same voltage as the logic power source VDD for a gate of the N-channel MOS transistor 28. It is therefore necessary to impress a voltage higher than the logic power source VDD to the gate of the N-channel MOS transistor 28. For the purpose of controlling the N-channel MOS transistor 28 with the heater voltage VH, therefore, circuits such as a resistance 25, the N-channel MOS transistors 26 and 27 and a P-channel MOS transistor 29 are provided in the driving circuit section 202.
However, when the source withstanding voltage of all stages of P-channel MOS transistors of this N-channel MOS transistor 28 is lower than the voltage value of the heater power source VH, direct connection of the heater power source VH to the P-channel MOS transistor 29 would result in breakage of the P-channel MOS transistor 29. This is why the heater power source VH is reduced by a prescribed value by means of the voltage drop circuit section 905 and then impressed onto the source of the P-channel MOS transistor 29.
An example of the rank resistance measuring circuit section 906 is illustrated in FIG. 13. As shown in FIG. 13, the rank resistance measuring circuit section 906 comprises resistances 31 to 33, a rank resistance 34, and an operational amplifier 35. The logic power source VDD entered into the rank resistance measuring circuit section 906 is divided into the resistances 31 and 32, and entered into a non-reverse input terminal of the operational amplifier 35. The voltage value thereof is amplified by a gain based on the resistance values of the resistance 33 and the rank resistance 34 and output as an output voltage (RANK). If the resistance values of the resistances 31 to 33 are known, therefore, it is possible to determine a resistance value of the rank resistance 34 from this output voltage. The rank resistance measuring circuit section 906 also has a configuration in which constant current I0 flows, irrespective of the operating state of the recording head, since the logic power source VDD is divided by the resistances 31 and 32.
A typical temperature measuring circuit section 907 is illustrated in FIG. 14. As shown in FIG. 14, the temperature measuring circuit section 907 comprises resistances 41 to 43, a diode temperature sensor 44, and an operational amplifier 45. The temperature measuring circuit section 907 has a circuit configuration in which the rank resistance 34 in the rank resistance measuring circuit section 906 shown in FIG. 13 is replaced by the diode temperature sensor 44. Temperature is measured by use of the fact that the positive-direction voltage of the diode temperature sensor varies with temperature. In the temperature measuring circuit section 907 also, in which the logic power source VDD is divided by the resistances 41 and 42, constant current I0 flows, irrespective of the operating state of the recording head (that is, current flows even during non-operation of the heater which is the energy converting element for converting electric energy into printing energy).
In general, when manufacturing a substrate for a recording head comprising a semiconductor substrate as described above, an inspection is carried out to see whether or not insulation is ensured between the wiring for impressing the source voltage, including the logic power source VDD and the heater power source VH, and the other circuit elements. This inspection is carried out by confirming whether or not a leak current is produced through impression of a voltage to such source voltages as the logic power source VDD and the heater power source VH.
However, constant current as a reference current flows through the voltage drop circuit section 905, the rank resistance measuring circuit section 906, and the temperature measuring circuit section 907 described above immediately upon impressing source voltages such as the logic power source VDD and the heater power source VH.
As a result, along with the tendency toward forming not only the heating resistors but also various circuits on the element substrate, with improvement of functions of the ink-jet recording apparatus, it is impossible to accurately measure the leak current with the conventional recording head substrate when a circuit permitting flow of constant current is formed on the element substrate 101.
The aforementioned conventional substrate for a recording head therefore has a problem in that, when forming a circuit through which current flows, together with heating resistors, current is produced immediately upon impression of a source voltage such as a logic power source and a heater power source, and inspection of the operating state of the energy converting element is carried out along with impression of a voltage onto the head. It is therefore impossible to accurately measure the leak current.
An object of the present invention is therefore to provide a substrate for a recording head that, even during non-operation of the energy converting element, and even when a circuit allowing flow of constant current upon impression of voltage of the head is formed together with the heating resistors, permits accurate measurement of leak current.
To achieve the aforementioned object, the present invention provides a substrate for a recording head used as a recording head for conducting printing on a recording medium, having an energy converting element for converting electric energy into printing energy, and a circuit through which current flows upon impression of a source voltage, irrespective of the operating state of the energy converting element, wherein there is provided a current cutoff means for cutting off current to the circuit in response to an entered control signal.
According to the invention, when the control signal becomes active, the current cutoff circuit cuts off current in the circuit through which constant current flows upon impressing the source voltage. When measuring the leak current to see whether or not insulation is ensured between the wiring for the source voltage and the other circuit elements of the substrate for a recording head, the constant current is cut off by making the control signal active. In a normal operating state, the leak current can be accurately measured even when a circuit through which a constant current flows is formed, together with heating resistors, on the element substrate.
The above-mentioned control signal may be a reset signal for achieving a standby state of a printing operation.
According to the present invention, in a standby state of a recording apparatus in which a printing operation is not carried out, the reset signal becoming active causes the current cutoff circuit to operate, thereby permitting cutting off a part of the standby current (current consumed in standby state). It is thus possible to curtail the power consumption. In the invention, furthermore, the reset signal is used as a control signal for controlling the current cutoff circuit. It is therefore not necessary to increase the number of terminals for connecting the substrate for the recording head and the wiring substrate, and the current cutoff circuit can be provided without an increase in cost.
The reset signal may be pulled down or pulled up so that the reset signal becomes active when cut off from outside.
According to the invention, the reset signal is pulled up or pulled down so that the reset signal becomes active when the recording head is cut off from the recording apparatus. Therefore, even when connection between the recording head and the recording apparatus becomes defective or cut off, the reset signal becomes active, thus making it possible to prevent wrong printing.
According to another substrate for a recording head of the invention, the circuit through which current flows upon impression of a source voltage, irrespective of the operating state of the energy converting element, may be a voltage drop circuit for reducing the source voltage to a prescribed value, a rank resistance measuring circuit for measuring a resistance value of a rank resistance provided for measuring a dispersion of resistance values of heating resistors resulting from manufacture, or a temperature measuring circuit. The current cutoff means may be provided in the circuit through which current flows upon impression of a source voltage, irrespective of the operating state of the energy converting element.
The energy converting element for converting electric energy into printing energy may be an energy converting element for converting electric energy into discharge energy for discharging a liquid.
The recording head of the invention comprises any of the above-mentioned substrates for a recording head, and a wiring substrate connected to the substrate for the recording head via a bonding wire.
Furthermore, the recording head of the invention may comprise a plurality of discharge ports discharging a liquid, and members forming a plurality of liquid channels communicating with the discharge ports.
The recording apparatus of the invention comprises the above-mentioned recording head, driving signal supplying means which supplies to the recording head a driving signal for driving the recording head, and recording medium conveying means for conveying a recording medium onto which printing is performed by the recording head.
The invention provides an inspecting method of a substrate for a recording head for inspecting whether or not insulation is ensured between wiring of a source voltage and other circuit elements by use of the above-mentioned substrate for a recording head, comprising:
a step of impressing a source voltage, making a control signal active and making a signal for controlling other logical circuits inactive;
a step of measuring a current value of the current produced upon impressing a source voltage, irrespective of the state of operation of the energy converting element; and
a step of, when the current value is a certain value or higher, determining that insulation is not ensured between wiring for impressing the source voltage and a circuit element which should normally not be connected thereto, and when the current value is lower than the certain value, determining that insulation is ensured between the wiring for impressing the source voltage and a circuit element which should normally not be connected thereto.
In the inspecting method of a substrate for a recording head of the invention, the control signal may be a reset signal for achieving a standby state of a printing operation.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.